This invention relates to compression release engine brakes, and more particularly to improved structures for coupling the slave pistons in such engine brakes to the exhaust valves in the associated internal combustion engine.
Compression release engine brakes or retarders are well known as shown, for example, by Jakuba et al. U.S. Pat. No. 4,473,047. Such devices typically operate by opening an exhaust valve in a cylinder in the internal combustion engine associated with the brake near top dead center of the compression stroke of that cylinder. This releases gas compressed during the compression stroke and prevents the work of compression from being recovered during the subsequent "power" stroke of the cylinder. In effect, the engine brake, while it is on, converts the engine from a power source to a power consuming gas compressor. This power consumption enables the engine to help slow down the associated vehicle, thereby saving wear on the vehicle's normal wheel brakes.
The typical compression release engine brake produces the exhaust valve openings described above by using a hydraulic circuit to pick up an appropriately timed motion from another part of the engine and to transfer that motion to the exhaust valve to be opened. A master piston in this hydraulic circuit receives the mechanical input from the engine. The hydraulic circuit transmits that input to a slave piston in the circuit. The slave piston moves in response to the transmitted input, thereby producing a mechanical output which is coupled to the exhaust valve in order to open that valve.
The force which must be transmitted from the slave piston to the exhaust valve is typically quite high. This has made it necessary to give careful attention to the design of the drive train between the slave piston and the associated exhaust valve or valves. It is known to have the slave piston contact the end of the exhaust valve stem, the exhaust valve bridge (where there are two exhaust valves per cylinder), or the end of the exhaust valve rocker arm adjusting screw. However, each of these known structures may have one or more disadvantages. It may be difficult to design the engine brake so that the slave piston is always properly aligned with the relatively small end of an exhaust valve stem or the similarly small end of a rocker arm adjusting screw. If such relatively small surfaces are to be used to transmit the large forces necessary in engine brakes, it is very important to achieve proper alignment. Any misalignment reduces the areas in contact with one another, thereby further increasing the stress on parts that are already highly stressed. With regard to using the exhaust valve bridge, it may be difficult to design the engine brake so that the slave piston contacts that bridge in a perfectly balanced way. If such balance is not achieved, the exhaust valve bridge may tend to cock and therefore wear unsymmetrically or otherwise malfunction. The exhaust valve bridge may also be surrounded by other structures, making it difficult to design an engine brake slave piston that can reach it.
Commonly assigned Hu U.S. Pat. No. 5,165,375 shows a master piston having a rigidly attached push rod with a swivel foot mounted on the spherically convex end of the push rod. The swivel foot bears on the engine part which provides the mechanical input to the engine brake. The load on the master piston drive train, however, is typically substantially less than the load on the slave piston drive train.
Commonly assigned Reich U.S. Pat. No. 5,195,489 shows a structure in which the slave (or master) piston has a push rod that can rock in a socket in the associated slave piston. The other end of the push rod bears on a rocker arm via a foot mounted in swivel fashion on the spherically convex end of the push rod. This structure works well but it may be more complicated and expensive than is necessary in some situations.
In view of the foregoing it is an object of this invention to improve and/or simplify the structures used in the slave piston drive trains of compression release engine braking systems.